1. Field of the Invention
This invention relates to a polyisocyanate composition based on toluene diisocyanate which can be used as a binder in a spray application without undue physiological hazard.
2. Description of the Prior Art
Urethane modified polyisocyanates are known to the art and find use as adhesives and binders. Such compounds are often prepared from toluene diisocyanate which is more economical (particularly on an NCO equivalent basis) than other commercial diisocyanates and which improves processing and urethane physical properties. However, such products normally contain several percent by weight of unreacted monomeric toluene diisocyanate. This free toluene diisocyanate constitutes a physiological hazard to workers when the product is used, particularly so in spray applications. Attempts to reduce the free toluene diisocyanate content by more complete reaction results in products of higher viscosity which are more difficult to use.
In U.S. Pat. No. 4,061,662, residual free toluene diisocyanate is removed from a urethane prepolymer by adsorbtion with type X zeolite molecular sieves. However, this procedure adds to the cost of the product in equipment, processing, and raw material costs.
I have found that these prior art problems are overcome and the desired product can be achieved by the process and product of this invention.